Industrial processing of polymers by low-pressure plasmas:: the role of VUV radiation

The use of low-pressure plasmas for materials processing, pioneered by the semiconductor industry since the 1960s, is now also a commercial reality in technologies which make extensive use of plastics (automotive, aerospace, packaging, pharmaceutical, textile, and other industries). A large fraction of these processes involve the surface modification of polymers for improved adhesion, and many of these use air or oxygen plasma to incorporate polar functional groups into the polymer surfaces. Interaction mechanisms between a plasma and a polymer surface are very complex, for they include synergistic effects of physical bombardment by energetic particles and by ultraviolet photons, and resulting chemical reactions at and below the surface. In this article we present an overview of plasma surface modification of polymers, in which rye identify the main variables for process control, illustrated by examples. We then show, on hand of a series of specially designed experiments, how the effects of ultraviolet photons generated in the plasma can be assessed separately from those of other energetic and reactive species, especially in the case of oxidizing plasmas. Finally, we comment on the merits and drawbacks of industrial plasma processes in comparison with other competing technologies, especially those based on ultraviolet radiation. (C) 1999 Elsevier Science B.V. All rights reserved.